Capillairedrukcurves

Capillairedrukcurves, often translated as capillary pressure curves, are graphical representations used in soil science, petroleum engineering, and hydrology to describe the relationship between capillary pressure and the wetting or non-wetting fluid saturation within a porous medium. Capillary pressure is defined as the pressure difference across the interface between two immiscible fluids, such as water and oil, within the pores of a material. This pressure arises from the surface tension forces at the fluid-fluid interface and the contact angle between the fluids and the pore walls.

The curves typically plot capillary pressure on the vertical axis and fluid saturation (usually of the wetting phase, like water) on the horizontal axis. At low wetting phase saturations, capillary pressure is high, indicating that significant energy is required to displace the wetting phase from the narrow pore throats. As the wetting phase saturation increases, the capillary pressure generally decreases. This is because the larger pores and channels become increasingly filled with the wetting phase, and the interface area between the fluids reduces. The shape and steepness of the capillary pressure curve are influenced by the pore size distribution of the porous medium. Fine-grained soils with a wide range of pore sizes will exhibit a more gradual curve, while materials with uniform pore sizes will show a sharper transition. These curves are crucial for understanding fluid flow, displacement processes, and reservoir characterization in various subsurface applications.